What is responsible for the seedling that bloomed 2 stalks beginning July 18? Then, I had six cultivars (mostly seedlings) that started bloom in August. Night temperatures didn't drop below 70 F until the last week of Aug. (for the required six consecutive nights.)

<<As you didn't get this condition until fall, this will be your limiting condition.>>

I understand that this is what triggers the fall cycle. Since it didn't limit the ones above, I'm wondering why the irises that are capable of doing the same, did not do so. They should not be limited by the need for falling temperatures!

You can't get rebloom until there is bud set. That depends on temperature, ie 6 nights with min 59-68F. (of course variations around this average) As you didn't get this condition until fall, this will be your limiting condition.

Chuck, I knew that I had high night temperatures. There were few nights below 70 degrees (F) all summer--over two months. None with six in a row. I didn't expect much bloom on the cycle rebloomers (fall.) I did hope for bloom on the summer rebloomers, or early fall rebloomers, since I watered them through the summer.

<<A plant can have genetics for rebloom, but not rebloom in a certain climate as environmental conditions are not suitable, or more likely secondary genetic factors in combintion are not suitable to trigger rebloom for that climate.>>

This seems to be the case in my garden for sure. Many of the irises that are reputed to be very good rebloomers all over the country, haven't been happy in my current garden. Even this year, with altered conditions the rebloom was very limited. There were many wasted stalks on plants that, theoretically, should have bloomed much earlier. It could have been the results of the two months with the relentless high & low temperatures for two months, but I have a feeling there is something more. Maybe the secondary needs?

We may need a reminder of the secondary genetic factors/needs you speak about. Are we talking modifiers here? Soil condition may be as important as climate.

<<There are four genetic systems for rebloom. (From what I can tell at moment) These are all different , and don't sem to be complemetal or cumulative. So they don't add to each other. >>

I seem to remember you stating that some are dominant over others. You don't believe two or more rebloom genes can transfer to the same plant? (Just restating in a different form.)

If the "preferntial Rebloomers" have a long enough growing season in your climate, then they would rebloom in your garden.

I have noted some more northern gardens that can do this. But they have a long growing time between last frost in spring and first hard frost of fall.

To tell if you climate is suitable for this type of rebloom, grow some of these plants. Don't count any fall bloom in year of acquisition. But again, in colder areas, they will likely be racing against frost.

There are four genetic systems for rebloom. (From what I can tell at moment) These are all different , and don't sem to be complemetal or cumulative. So they don't add to each other.

So these secondary factors can be added from combining differernt genetic rebloomers (or from any other plant having these secondary genetics). But still only earliest rebloom trigger will give you rebloom.

A plant can have genetics for rebloom, but not rebloom in a certain climate as environmental conditions are not suitable, or more likely secondary genetic factors in combintion are not suitable to trigger rebloom for that climate.

Lloyd Zurbigg found this. He made a lot of rebloom crosses here in Canada, but had little sucesse. When he moved to USA, these same seedlings rebloomed for him.

I'm not convinced yet that in my long growing season some of the
"summer" bloomers here don't also have what you are calling preferential
vernalization genetic makeup.

Plus I thought that there are multiple genes contributing to rebloom?
So it's not just presence/absence of a particular type of vernalization
requirement. Are you positive it's a different gene and not just a
different suite of max/min & duration of temperature requirements?

Takes a lot of crosses to answer that question, I think.

Most of the CA and Oz (and esp OR) rebloomers are in what is more or
less zone 8, close enough to my zone 7b temperatures. Now if we can
just combine wet/humid enthusiasm with their dry summer/low humidity
selection, and if all the other genes that contribute to rebloom match up...

I agree that it seems unlikely to work for you that far north, Chuck.
Wait for global warming? ;-)

> Final Episode seems to be one of those iris that rebloom when it has an extended period of warm weather while in a mature state. A class of rebloomers that are basically "prefernial vernalization" as versus "Obligatory vernalization".
>
> Obligatory vernalization means that the plant has to have vernalization before blooming. Preferntial vernalization have a secondary sytem, that enables it to rebloom when it has had a long period while sitting at maturity. These types will rebloom in Australia and California, but not else where.
>
> So breeding with it will perhaps produce California rebloomers, but unles you live in a climate that has an apropriate long warm growth period, it won't contribute much to a rebloom program.
>
> Chuck Chapman